Air Watts are an instantaneous measurement of both suction and airflow simultaneously at a given orifice size. It's a snapshot in time. Suction and airflow will be different for every orifice size with suction increasing and airflow decreasing as the size of the orifice is reduced.
Suction work rate measures the volume of air that flows through the opening of a hose over a period of time, multiplied by the sealed suction also measured at the end of the hose and that product is multiplied by a constant. Measuring the total volume of air over a period of time reduces the errors inherent in trying to capture an instantaneous airflow measurement so you don't have to try to normalize for the different speeds of air in a tube or pipe with turbulent airflow as you encounter measuring air watts.